This invention relates to a high performance package providing fluid cooling means for relatively high density semiconductor integrated circuits. The objects of high performance packages in general are severalfold:
(1) the protection of semiconductor chips, i.e. integrated circuits, from contamination such as moisture, salt and the like and mechanical stresses that might fracture the chips or alter component values;
(2) the provision of electrical power to the chips;
(3) the removal of waste heat caused by the operation of the chips;
(4) interconnection of chips by means of large numbers of electrical signal transmission lines;
(5) since integrated circuits are typically simply components of computers, provision must be made for the signals, power and cooling connections of the package to connect with other portions of the computer;
(6) provision must be made for repair of failed chips with minimum disturbance of parts in the package not requiring repair; and
(7) the packing of chips as densely as possible to shorten the length of signal transmission lines between chips thereby increasing overall speed of a computer.
Heretofor, numerous proposals have been made for the design of semiconductor chip packages with heat sinks for waste heat removal purposes. For example, a package module for a single chip was proposed in IBM Technical Disclosure Bulletin, Volume 24, No. 1A, June 1981. Therein it was suggested that the chip be back-bonded to a high thermal conductivity material heat sink. Electrical and power connections to the chip were made using thin film wiring and flexible leads.
Air-cooling fins for purposes of cooling high density integrated circuits package also have been proposed. For example, the article entitled "High Thermal Conduction Package Technology for Flip Chip Devices" by Kohara, et al., appeared in IEEE Transactions on Components, Hybrids and Manufacturing Technology, Volume CHMT-6, No. 3, September 1982. However, air-cooling has severe limitations in that only small amounts of waste heat may be dissipated, and present and future design considerations for very high density chip packages necessitate removal of significantly higher amounts of heat to maintain junction temperatures at suitable levels.
Fluid-cooled integrated circuit packages offer distinct advantages based on simplicity, efficiency and lack of corrosive qualities within a closed system. Such a package is disclosed in an article entitled "Integral Liquid-Cooling System Simplifies Design of Densely Packaged Computer" by Edward A. Wilson, Electronics, Jan. 26, 1984, pages 123 et seq. Here an integral cooler is proposed to which micro packages may be added or removed as desired. The micro packages are mounted on printed circuit boards serving as back panels in turn attached to the integral coolers. Water enters mainfolds at the bottom of the coolers and flows in parallel through the columns of the coolers to be collected at the top.
Another water-cooled system is the IBM Cold-Plate Cooled Thermal Conduction Module (TCM) illustrated in the article entitled "Thermal Management of Large Scale Digital Computer" by Chu et al., The International Society For Hybrid Microelectronics, Volume 7, No. 3, September 1984. The TCM consists of a large number of integrated circuit chips with a spring-loaded piston touching each chip and a water-cooled cold plate bolted to the package housing. Heat is conducted from the chips into the pistons and then through the housing and out to the water-cooled plate. The thermal paths from chips to piston and from piston to housing may be enhanced by the use of helium gas.
Variations on the TCM form of package are illustrated in U.S. Patents Nos. 4,381,032 and 4,531,146. Both patents illustrate high density integrated circuit package devices having cooling chambers. A fluid coolant is passed through the chamber under pressure. The cooling chamber in each case is adjacent to and in biased contact with integrated circuits so as to conduct heat away therefrom. These packages have certain serious drawbacks, one being the relatively large physical size required to accommodate even a small number of densely packed integrated circuits. Furthermore, while the packages may accommodate relatively large amounts of cooling fluid, there is a small amount of heat exchange surface between each integrated circuit package and the coolant presenting a significant limitation on the total amount of waste heat that may be removed in each package.
The use of integral liquid-cooled heat sinks in multi-chip systems has been the subject of an in-depth review by David B. Tuckerman as presented in his dissertation entitled Heat-Transfer Microstructures for Integrated Circuits, Stanford University, February 1984. Also, Dr. Tuckerman and Dr. R. F. W. Pease have collaborated in investigating compact, high-performance forced liquid cooling of planar integrated circuits as reported, for example, in an article entitled "High-Performance Heat Sinking for VLSI, " IEEE Electron Device Letters, Volume EDL-2, No. 5, May 1981. They have suggested the use of silicon as a suitable heat sink material into which may be sawed or etched microscopic channels for cooling fluid to flow to remove waste heat from the integrated circuits. Because of the small size of the channels, they are referred to as "microchannels". Cooling fluid may be uniformly distributed among the channels by means of headers or manifolds communicating with an external source of the fluid. Also suggested is a microcapillary thermal interface concept wherein capillary channels are provided in the heat sink surface adjacent to each integrated circuit. A limited amount of interfacial liquid partially fills the capillaries to provide a well-defined attractive (suction) force due to the liquid's surface tension. The capillary action promotes closer contact of the integrated circuits with the heat sink for improved heat exchange function.